Production of broad molecular weight polyethylene

ABSTRACT

Broad molecular weight polyethylene and polyethylene having a bimodal molecular weight profile can be produced with chromium oxide based catalyst systems employing alkyl silanols. The systems may also comprise various organoaluminum compounds. Catalyst activity and molecular weight of the resulting polyethylene may also be tuned using the present invention.

TECHNICAL FIELD

[0001] The present invention relates to the use of chromium-basedcatalysts with alkyl silanols such as triphenyl silanol with or withoutaluminum alkyl activators. The use of aluminum alkyls and alkyl silanolsallows for the control of polymer molecular weight and molecular weightdistribution and results in a catalyst with behavior similar tosilylchromate on silica catalyst. Bimodal polyethylene may be producedwith the present invention.

BACKGROUND OF THE INVENTION

[0002] Ethylene polymers have been used generally and widely as resinmaterials for various molded articles and are required to have differentproperties depending on the molding method and purpose. For example,polymers having relatively low molecular weights and narrow molecularweight distributions are suitable for articles molded by an injectionmolding method. On the other hand, polymers having relatively highmolecular weights and broad molecular weight distributions are suitablefor articles molded by blow molding or inflation molding. In manyapplications, medium-to-high molecular weight polyethylenes aredesirable. Such polyethylenes have sufficient strength for applicationswhich call for such strength (e.g., pipe applications), andsimultaneously possess good processability characteristics.

[0003] Ethylene polymers having broad molecular weight distributions canbe obtained by use of a chromium catalyst obtained by calcining achromium compound carried on an inorganic oxide carrier in anon-reducing atmosphere to activate it such that at least a portion ofthe carried chromium atoms is converted to hexavalent chromium atoms(Cr+6). This is commonly referred to in the art as the Phillipscatalyst. The respective material is impregnated onto silica, fluidizedand heated in the presence of oxygen to about 400° C. -860° C.,converting chromium from the +3 oxidation state to the +6 oxidationstate. A second chromium catalyst used for high density polyethyleneapplications consists of silylchromate (bis-triphenylsilyl chromate)absorbed on dehydrated silica and subsequently reduced withdiethylaluminum ethoxide (DEALE). The resulting polyethylenes producedby each of these catalysts are different in some important properties.Chromium oxide-on-silica catalysts have good productivity (g PE/gcatalyst), also measured by activity (g PE/g catalyst-hr) but producepolyethylenes with molecular weight distributions lower than thatdesired for certain applications. Silylchromate-based catalysts producepolyethylenes with desirable molecular weight distributioncharacteristics (broader molecular weight distribution with a highmolecular weight shoulder on molecular weight distribution curve,indicative of two distinct molecular weight populations).

[0004] Monoi, in Japanese Patent 200202412 discloses the use ofinorganic oxide-supported Cr+6-containing solid components (A) preparedby sintering under nonreducing conditions, dialkylaluminum functionalgroup-containing alkoxides (B), and trialkylaluminum (C). The resultingethylene polymers are said to possess good environmental stress crackresistance and good blow molding creep resistance. U.S. application SER.No. 2002042428 discloses a method of ethylene polymerization inco-presence of hydrogen using a trialkylaluminum compound-carriedchromium catalyst (A), wherein the chromium catalyst is obtained bycalcination-activating a Cr compound carried on an inorganic oxidecarrier in a non-reducing atmospheric to convert Cr atoms into thehexavalent state and then treating A with a trialkylaluminum compound inan inert hydrocarbon solvent and removing the solvent in a short time.

[0005] Hasebe et al. Japanese Patent 2001294612 discloses catalystscontaining inorganic oxide-supported Cr compounds calcined at 300°C.-1100° C. in a nonreducing atmosphere, R_(3-n)AlL_(n) (R=C1-12 alkyl;L=C1-8 alkoxy, phenoxy; 0 <n <1), and Lewis base organic compounds. Thecatalysts are said to produce polyolefins with high molecular weight andnarrow molecular weight distribution.

[0006] Hasebe et al., in Japanese Patent 2001198811 disclosespolymerization of olefins using catalysts containing Cr oxides(supported on fire resistant compounds and activated by heating undernonreductive conditions) and R_(3-n)AlL_(n) (R=C1-6 alkyl; L=C1-8alkoxy, phenoxy; n>0.5 but <1). Ethylene is polymerized in the presenceof SiO₂-supported CrO₃ and a reaction product of a 0.9:1 MeOH-Et₃Almixture to give a polymer with melt index 0.18 g/10 min at 190 ° C.under 2.16-kg load and 1-hexene content 1.6 mg/g-polymer.

[0007] Da, et al, in Chinese Patent 1214344 teaches a supportedchromium-based catalyst for gas-phase polymerization of ethyleneprepared by impregnating an inorganic oxide support having hydroxylgroup on the surface with an inorganic chromium compound aqueoussolution; drying in air; activating the particles in oxygen; andreducing the activated catalyst intermediate with an organic aluminumcompound. 10 g commercial silica gel was mixed with 0.05 mol/L CrO₃aqueous solution, dried at 80-120 ° C. for 12 h, baked at 200 ° C. for 2h and 600° C. for 4 h, reduced with 25% hexane solution ofdiethylethoxyaluminum to give powder catalyst with Cr content 0.25% andAl/Cr ratio of 3.

[0008] Durand, et al, U.S. Pat. No. 5,075,395, teaches a process forelimination of the induction period in the polymerization of ethylene bybringing ethylene in contact under fluidized-bed polymerizationconditions and/or stirred mechanically, with a charge powder in thepresence of a catalyst comprising a chromium oxide compound associatedwith a granular support and activated by thermal treatment, thiscatalyst being used in the form of a prepolymer. The Durand process ischaracterized in that the charge powder employed is previously subjectedto a treatment by contacting the said charge powder with anorganoaluminum compound, in such a way that the polymerization starts upimmediately after the contacting of the ethylene with the charge powderin the presence of the prepolymer.

[0009] McDaniel, in U.S. Pat. No. 4,559,394 teaches the polymerizationof olefins using activated chromium catalysts and tertiary alcohols.These patents teach the addition of alcohols to chromium oxide toimprove chromium distribution. McDaniel adds the tertiary alcohol priorto catalyst activation. Interestingly, McDaniel teaches that silanols donot work to achieve this end.

[0010] U.S. Patent Nos. 4,454,242 and 4,451,573 to Ikegami, et al,employ silanols in conjunction with chromium oxide catalysts treatedwith zirconium or titanium and alkylmagnesium compounds to make improvedenvironmental stress crack resistance (ESCR) products.

[0011] Chromium catalysts based on chromocene and silanols have beenprepared and deposited on silica to increase catalyst activity as taughtin U.S. Pat. No. 4,153,576 to Karol et al. U.S. Pat. Nos. 3,767,635;3,629,216; and 3,759,918, assigned to Mitsubishi Chemical Industries,Ltd., teach the addition of pentaalkylsiloxyalanes to supported chromiumoxide catalysts to make useful polyethylenes.

[0012] Chromium oxide (CrOx) based catalysts have high activity withmoderate induction times and produce polymers with high molecularweights and intermediate molecular weight distributions.Silylchromate-based catalysts have poorer activity, but produce polymerswith a broader molecular weight distribution. Silylchromate catalystsare typically more costly than chromium oxide catalysts. It would bedesirable to have a method that allows for the tuning of chromium oxidebased catalysts such that the polymers produced by them approach thecharacteristics of polymers produced using silylchromate-basedcatalysts. For background information regarding silylchromate catalysis,see e.g., U.S. Pat. Nos. 3,324,095 and 3,324,101 to Carrick et al. Theprior art lacks an inexpensive, facile method for modifying a chromiumoxide catalyst such that polymer produced by it can be variably tuned toapproach polymer produced by silylchromate-based catalyst systems.Additionally, the prior art is devoid of any teaching of the use ofsilanols in a two-catalyst system to obtain polymers with bimodalmolecular weight distribution profiles.

[0013] While the prior art contains these and other examples of the useof modified Phillips-type catalysts, there has not yet been disclosed amethod for the control of molecular weight distribution. The presentinvention provides a method for the production of polyethylenecharacterized by the control of both the molecular weight and thebreadth of molecular weight distribution. The present invention alsoprovides a method to produce a bimodal polyethylene through the use oftwo chromium-based catalyst systems.

SUMMARY OF THE INVENTION

[0014] The present invention is directed to a system and method for thepolymerization ethylene using chromium-based catalysts with control ofmolecular weight and molecular weight distribution. It also provides forthe production of bimodal polyethylene through the use of catalystsystems having two chrome catalysts.

[0015] In one aspect of the present invention, there is a supportedchromium catalyst comprising chromium oxide, a silica-containing supportcomprising silica selected from the group consisting of silica having(a) a pore volume of about 1.1-1.8 cm³/g and a surface area of about245-375 m²/g, (b) a pore volume of about 2.4-3.7 cm³/g and a surfacearea of about 410-620 m²/g, and (c) a pore volume of about 0.9-1.4 cm³/gand a surface area of about 390-590 m²/g, and an alkyl silanol, whereinthe supported chromium catalyst is activated at 400-860° C., prior tothe addition of said alkyl silanol.

[0016] In another embodiment, the catalyst further comprises titaniumtetraisopropoxide. In another embodiment, the catalyst further comprisesan organoaluminum compound. In a specific embodiment having anorganoaluminum compound, the activated chromium catalyst is treatedfirst with the alkyl silanol and then with the organoaluminum compound.In another specific embodiment having an organoaluminum compound, thesilica has a pore volume of about 2.4-3.7 cm³/g and a surface area ofabout 410-620 m²/g and said organoaluminum compound is an alkyl aluminumalkoxide compound. In yet another specific embodiment having anorganoaluminum compound, the silica has a pore volume of about 1.1-1.8cm³/g and a surface area of about 245-375 m²/g, and said organoaluminumcompound is an alkyl aluminum alkoxide compound. In another specificembodiment having an organoaluminum compound, the organoaluminumcompound is added in-situ. In yet another specific embodiment having anorganoaluminum compound, the catalyst further comprises at least asecond chromium-based compound. In a specific embodiment having at leasta second chromium-based compound, the second chromium-based compound isa chromium oxide on silica or an organoaluminum-reduced chromium oxideon silica.

[0017] In another embodiment of the catalyst having an organoaluminumcompound, the alkyl silanol or the organoaluminum compound or both thealkyl silanol and the organoaluminum compound are added in-situ. In aspecific embodiment, the alkyl silanol and the organoaluminum compoundare pre-mixed prior to said in-situ addition.

[0018] In another embodiment of the catalyst having an organoaluminumcompound, the organoaluminum compound is an alkyl aluminum alkoxidecompound. In a specific embodiment, the alkyl aluminum alkoxide compoundis diethyl aluminum ethoxide. In another specific embodiment, thecatalyst having an alkyl aluminum alkoxide compound is formed by the insitu addition of said alkyl aluminum alkoxide compound. In a specificembodiment, the alkyl aluminum alkoxide compound is diethyl aluminumethoxide.

[0019] In another embodiment of the catalyst having an organoaluminumcompound, the organoaluminum compound is an alkyl aluminum compound. Ina specific embodiment, the alkyl aluminum compound is selected from thegroup consisting of triethyl aluminum, tri-isobutyl aluminum, andtri-n-hexyl aluminum. In another specific embodiment, the catalyst isformed by the in situ addition of the alkyl aluminum compound. In yetanother specific embodiment, the alkyl aluminum compound added insitu istri-isobutyl aluminum.

[0020] In another embodiment of the supported chromium catalyst, thecatalyst is activated at 600-860° C. In another embodiment of thesupported chromium catalyst, the alkyl silanol is triphenyl silanol.

[0021] In the present invention, there is also a supported chromiumcatalyst comprising chromium oxide, a silica-containing supportcomprising silica selected from the group consisting of silica having(a) a pore volume of about 1.1-1.8 cm³/g and a surface area of about245-375 m²/g, (b) a pore volume of about 2.4-3.7 cm³/g and a surfacearea of about 410-620 m2/g, and (c) a pore volume of about 0.9-1.4 cm³/gand a surface area of about 390-590 m²/g and, an organoaluminumcompound, wherein the supported chromium catalyst is activated at400-860° C.

[0022] In a specific embodiment, the organoaluminum compound is diethylaluminum triethylsiloxide. In another embodiment, the catalyst furthercomprises titanium tetraisopropoxide.

[0023] Also in the present invention, there is a supported chromiumcatalyst comprising chromium oxide, a silica-containing supportcomprising silica selected from the group consisting of silica having(a) a pore volume of about 1.1-1.8 cm³/g and a surface area of about245-375 m²/g, (b) a pore volume of about 2.4-3.7 cm³/g and a surfacearea of about 410-620 m²/g, and (c) a pore volume of about 0.9-1.4 cm³/gand a surface area of about 390-590 m²/g wherein said supported chromiumcatalyst is activated at 400-860° C., and, a second chromium-basedcompound comprising silylchromate on silica treated with anorganoaluminum compound. In a specific embodiment, the chromium oxidecatalyst component is treated with an organoaluminum compound afteractivation. In another embodiment, the catalyst further comprisestitanium tetraisopropoxide.

[0024] In the present invention, there is also a process for producingan ethylene polymer comprising the steps of contacting ethylene underpolymerization conditions with a catalyst system, said catalyst systemcomprising chromium oxide, an alkyl silanol compound, and asilica-containing support comprising silica selected from the groupconsisting of silica having (a) a pore volume of about 1.1-1.8 cm³/g anda surface area of about 245-375 m²/g, (b) a pore volume of about 2.4-3.7cm³/g and a surface area of about 410-620 m²/g, and (c) a pore volume ofabout 0.9-1.4 cm³/g and a surface area of about 390-590 m²/g and,controlling one or more of catalyst activity, polymer Mz/Mw, polymerMw/Mn, and polymer density of the resulting ethylene polymer by varyingthe level of addition of said alkyl silanol.

[0025] In one embodiment of the process the polymer Mw/Mn is controlledto greater than about 15 and the polymer Mz/Mw is controlled to greaterthan about 5. In another embodiment of the process, the catalyst systemfurther comprises an organoaluminum compound. In a specific embodimentof the process where the catalyst system further comprisesorganoaluminum, the catalyst system further comprises at least a secondchromium-based catalyst. In a specific embodiment of the process wherethe catalyst system further comprises a second chromium-based catalyst,the second chromium-based compound is a chromium oxide on silica or anorganoaluminum-reduced chromium oxide on silica. In another specificembodiment of the process where the catalyst system further comprises asecond chromium-based catalyst, the organoaluminum compound is an alkylaluminum alkoxide. In another embodiment wherein the organoaluminumcompound is an alkyl aluminum alkoxide, the alkyl aluminum alkoxide isdiethylaluminum ethoxide. In another embodiment, the organoaluminumcompound is an alkyl aluminum compound. In another embodiment of theprocess using alkyl aluminum compound, the alkyl aluminum compound isselected from the group consisting of triethyl aluminum, tri-isobutylaluminum, and tri-n-hexyl aluminum. In another embodiment of theprocess, the catalyst system further comprises titaniumtetraisopropoxide.

[0026] In another embodiment, there is a process for producing anethylene polymer comprising the steps of contacting ethylene underpolymerization conditions with a catalyst system, said catalyst systemcomprising chromium oxide, a silica-containing support comprising silicaselected from the group consisting of silica having (a) a pore volume ofabout 1.1-1.8 cm³/g and a surface area of about 245-375 m²/g, (b) a porevolume of about 2.4-3.7 cm³/g and a surface area of about 410-620 m²/g,and (c) a pore volume of about 0.9-1.4 cm³/g and a surface area of about390-590 m²/g wherein the supported chromium catalyst is activated at400-860° C. and, a second chromium-based compound comprisingsilylchromate on silica treated with an organoaluminum compound and,controlling one or more of polymer molecular weight, polymer Mz/Mw,polymer Mw/Mn, and distribution of comonomer incorporation by varyingthe relative amount of each of the chromium oxide and the secondchromium-based compound. In another embodiment of the process thechromium oxide catalyst component is treated with an organoaluminumcompound after activation. In another embodiment, the catalyst systemfurther comprises titanium tetraisopropoxide.

[0027] There is also an ethylene polymer having a density of 0.918-0.970g/cm³ and a flow index (I21) of 1-500 and produced by the processcomprising the steps of contacting ethylene under polymerizationconditions with a catalyst system, the catalyst system comprisingchromium oxide, an alkyl silanol compound, and a silica-containingsupport comprising silica selected from the group consisting of silicahaving (a) a pore volume of about 1.1-1.8 cm³/g and a surface area ofabout 245-375 m²/g, (b) a pore volume of about 2.4-3.7 cm³/g and asurface area of about 410-620 m²/g, and (c) a pore volume of about0.9-1.4 cm³/g and a surface area of about 390-590 m²/g; and, controllingone or more of catalyst activity, polymer Mz/Mw, polymer Mw/Mn, andpolymer density of the resulting ethylene polymer by varying the levelof addition of the alkyl silanol.

[0028] In another embodiment, there is an ethylene polymer having adensity of 0.918-0.970 g/cm³ and a flow index (I21) of 1-500 andproduced by the process comprising the steps of contacting ethyleneunder polymerization conditions with a catalyst system, the catalystsystem comprising chromium oxide, an alkyl silanol compound, anorganoaluminum compound, and a silica-containing support comprisingsilica selected from the group consisting of silica having (a) a porevolume of about 1.1-1.8 cm³/g and a surface area of about 245-375 m²/g,(b) a pore volume of about 2.4-3.7 cm³/g and a surface area of about410-620 m²/g, and (c) a pore volume of about 0.9-1.4 cm³/g and a surfacearea of about 390-590 m²/g; and, controlling one or more of catalystactivity, polymer Mz/Mw, polymer Mw/Mn, and polymer density of theresulting ethylene polymer by varying the level of addition of the alkylsilanol.

[0029] In another embodiment, there is an ethylene polymer having adensity of 0.918-0.970 g/cm³ and a flow index (I21) of 1-500 andproduced by the process comprising the steps of contacting ethyleneunder polymerization conditions with a catalyst system, the catalystsystem comprising chromium oxide, an alkyl silanol compound, anorganoaluminum compound, at least a second chromium-based catalyst, anda silica-containing support comprising silica selected from the groupconsisting of silica having (a) a pore volume of about 1.1-1.8 cm³/g anda surface area of about 245-375 m²/g, (b) a pore volume of about 2.4-3.7cm³/g and a surface area of about 410-620 m²/g, and (c) a pore volume ofabout 0.9-1.4 cm³/g and a surface area of about 390-590 m²/g; and,controlling one or more of catalyst activity, polymer Mz/Mw, polymerMw/Mn, and polymer density of the resulting ethylene polymer by varyingthe level of addition of the alkyl silanol.

[0030] In another embodiment, there is an ethylene polymer having adensity of 0.918-0.970 g/cm³ and a flow index (I21) of 1-500 andproduced by the process comprising the steps of contacting ethyleneunder polymerization conditions with a catalyst system, the catalystsystem comprising chromium oxide, an alkyl silanol compound, anorganoaluminum compound, at least a second chromium-based catalystwherein the second chromium-based catalyst is a chromium oxide on silicaor an organoaluminum-reduced chromium oxide on silica, and asilica-containing support comprising silica selected from the groupconsisting of silica having (a) a pore volume of about 1.1-1.8 cm³/g anda surface area of about 245-375 m²/g, (b) a pore volume of about 2.4-3.7cm³/g and a surface area of about 410-620 m²/g, and (c) a pore volume ofabout 0.9-1.4 cm³/g and a surface area of about 390-590 m²/g; and,controlling one or more of catalyst activity, polymer Mz/Mw, polymerMw/Mn, and polymer density of the resulting ethylene polymer by varyingthe level of addition of the alkyl silanol.

[0031] In another embodiment, there is an ethylene polymer having adensity of 0.918-0.970 g/cm³ and a flow index (I21) of 1-500 andproduced by the process comprising the steps of contacting ethyleneunder polymerization conditions with a catalyst system, said catalystsystem comprising chromium oxide, a silica-containing support comprisingsilica selected from the group consisting of silica having (a) a porevolume of about 1.1-1.8 cm³/g and a surface area of about 245-375 m²/g,(b) a pore volume of about 2.4-3.7 cm³/g and a surface area of about410-620 m²/g, and (c) a pore volume of about 0.9-1.4 cm³/g and a surfacearea of about 390-590 m²/g wherein said supported chromium catalyst isactivated at 400-860° C.; wherein the chromium oxide catalyst componentis treated with an organoaluminum compound after activation and, asecond chromium-based compound comprising silylchromate on silicatreated with an organoaluminum compound and, controlling one or more ofpolymer molecular weight, polymer Mz/Mw, polymer Mw/Mn, and distributionof comonomer incorporation by varying the relative amount of each ofsaid chromium oxide and said second chromium-based compound.

[0032] The foregoing has outlined rather broadly the features andtechnical advantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims. The novel features which are believed to be characteristic ofthe invention, both as to its organization and method of operation,together with further objects and advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] For a more complete understanding of the present invention,reference is now made to the following descriptions taken in conjunctionwith the accompanying drawing, in which:

[0034]FIG. 1. Possible structure of chromium oxide-on-silica(“Phillips”) catalyst.

[0035]FIG. 2. Possible structure of silylchromate-on-silica catalyst.

[0036]FIG. 3. Effect of TPS on CrOx catalysts kinetic profile.

[0037]FIG. 4. Effect of TPS on CrOx catalyst polymer molecular weightdistribution.

[0038]FIG. 5. Effect of TPS on CrOx catalyst kinetic profile; 5A, CrOx;5B, Ti—

[0039] CrOx. FIG. 6. Effect of TES on CrOx catalyst kinetic profile.

[0040]FIG. 7. Kinetic profile of CrOx catalyst treated with TPS andDEALE.

[0041]FIG. 8. Effect of DEALSi on CrOx catalyst kinetic profile.

DETAILED DESCRIPTION OF THE INVENTION

[0042] As used herein, “a” or “an” is defined herein as one or more.

[0043] As used herein, “in situ,” in reference to the mode of additionof a component to the catalyst, is defined herein as addition to thecatalyst in the reactor. Therefore, when a catalyst component is addedin situ, it is added to the remaining catalyst components in the reactorand is not combined with the other catalyst components prior to theirtransport to the reactor. “In reactor” is synonymous with and usedinterchangeably herein with “in situ.”

[0044] As used herein, “in catalyst” or “on catalyst,” in reference tothe mode of addition of a component to the catalyst, is defined hereinas addition directly to the catalyst prior to introduction of thecatalyst to the reactor. Therefore, when a component is added to thecatalyst “in catalyst” or “on catalyst,” it is added to the othercatalyst components prior to the transport of the aggregate to thereactor.

[0045] As used herein, the term alkyl aluminum is defined as a compoundhaving the general formula R₃Al wherein R can be any of one to twelvecarbon alkyl or aryl groups. The R groups can be the same or different.

[0046] As used herein, the term alkyl aluminum alkoxide is defined as acompound having the general formula R₂-Al-OR wherein R can be any of oneto twelve carbon alkyl groups and OR is a one to twelve carbon alkoxy orphenoxy group. The R groups can be the same or different.

[0047] As used herein, the term “alkyl silanol” is defined as a compoundhaving the general formula R₃-Si-OH where R can be any of one to twelvecarbon alkyl groups or aryl groups. The R groups can be the same ordifferent.

[0048] As used herein, “DEALE” means diethyl aluminum ethoxide.

[0049] As used herein, “DEALSi” means diethylaluminum triethylsiloxideand is used to represent the reaction product of TEAL andtriethylsilanol.

[0050] As used herein, “TEAL” means triethyl aluminum.

[0051] As used herein, “TES” means triethylsilanol.

[0052] As used herein, “TIBA” means tri-isobutyl aluminum.

[0053] As used herein, “TPS” means triphenylsilanol.

[0054] As used herein, “TTIP” means titanium tetraisopropoxide.

[0055] As used herein, “M_(w)” is the weight-average molecular weight

[0056] As used herein, “M_(n)” is the number-average molecular weight.

[0057] As used herein, “M_(z)” is the z-average molecular weight.

[0058] As used herein, “molecular weight distribution” is equal toM_(w)/M_(n).

[0059] The invention is applicable to the polymerization of olefins byany suspension, solution, slurry, or gas phase process, using knownequipment and reaction conditions, and is not limited to any specifictype of polymerization system. Generally, olefin polymerizationtemperatures range from about 0° C. to about 300° C. at atmospheric,subatmospheric, or superatmospheric pressures. Slurry or solutionpolymerization systems may utilize subatmospheric or superatmosphericpressures and temperatures in the range of about 40° C. to about 300° C.A useful liquid phase polymerization system is described in U.S. Pat.3,324,095. Liquid phase polymerization systems generally comprise areactor to which olefin monomer and catalyst composition are added, andwhich contains a liquid reaction medium for dissolving or suspending thepolyolefin. The liquid reaction medium may consist of the bulk liquidmonomer or an inert liquid hydrocarbon that is nonreactive under thepolymerization conditions employed. Although such an inert liquidhydrocarbon need not function as a solvent for the catalyst compositionor the polymer obtained by the process, it usually serves as solvent forthe monomers employed in the polymerization. Among the inert liquidhydrocarbons suitable for this purpose are isobutane, isopentane,hexane, cyclohexane, heptane, benzene, toluene, and the like. Reactivecontact between the olefin monomer and the catalyst composition shouldbe maintained by constant stirring or agitation. The reaction mediumcontaining the olefin polymer product and unreacted olefin monomer iswithdrawn from the reactor continuously. The olefin polymer product isseparated, and the unreacted olefin monomer and liquid reaction mediumare recycled into the reactor.

[0060] The invention is, however, especially useful with gas phasepolymerization systems, with superatmospheric pressures in the range of1 to 1000 psi, preferably 50 to 400 psi, most preferably 100 to 300 psi,and temperatures in the range of 30 to 130 ° C., preferably 65 to 110°C. Stirred or fluidized bed gas phase polymerization systems areparticularly useful. Generally, a conventional gas phase, fluidized bedprocess is conducted by passing a stream containing one or more olefinmonomers continuously through a fluidized bed reactor under reactionconditions and in the presence of catalyst composition at a velocitysufficient to maintain a bed of solid particles in a suspendedcondition. A stream containing unreacted monomer is withdrawn from thereactor continuously, compressed, cooled, optionally partially or fullycondensed, and recycled into the reactor. Product is withdrawn from thereactor and make-up monomer is added to the recycle stream. As desiredfor temperature control of the polymerization system, any gas inert tothe catalyst composition and reactants may also be present in the gasstream. In addition, a fluidization aid such as carbon black, silica,clay, or talc may be used, as disclosed in U.S. Pat. No. 4,994,534.

[0061] The polymerization system may comprise a single reactor or two ormore reactors in series, and is conducted substantially in the absenceof catalyst poisons. Organometallic compounds may be employed asscavenging agents for poisons to increase the catalyst activity.Examples of scavenging agents are metal alkyls, preferably aluminumalkyls.

[0062] Conventional adjuvants may be used in the process, provided theydo not interfere with the operation of the catalyst composition informing the desired polyolefin. Hydrogen may be used as a chain transferagent in the process, in amounts up to about 10 moles of hydrogen permole of total monomer feed.

[0063] Polyolefins that may be produced according to the inventioninclude, but are not limited to, those made from olefin monomers such asethylene and linear or branched higher alpha-olefin monomers containing3 to about 20 carbon atoms. Homopolymers or interpolymers of ethyleneand such higher alpha-olefin monomers, with densities ranging from about0.86 to about 0.97 may be made. Suitable higher alpha-olefin monomersinclude, for example, propylene, 1-butene, 1-pentene, 1-hexene,4-methyl-l-pentene, 1-octene, and 3,5,5-trimethyl-1-hexene. Olefinpolymers according to the invention may also be based on or containconjugated or non-conjugated dienes, such as linear, branched, or cyclichydrocarbon dienes having from about 4 to about 20, preferably 4 to 12,carbon atoms. Preferred dienes include 1,4-pentadiene, 1,5-hexadiene,5-vinyl-2-norbornene, 1,7-octadiene, vinyl cyclohexene,dicyclopentadiene, butadiene, isobutylene, isoprene, ethylidenenorbornene and the like. Aromatic compounds having vinyl unsaturationsuch as styrene and substituted styrenes, and polar vinyl monomers suchas acrylonitrile, maleic acid esters, vinyl acetate, acrylate esters,methacrylate esters, vinyl trialkyl silanes and the like may bepolymerized according to the invention as well. Specific polyolefinsthat may be made according to the invention include, for example, highdensity polyethylene, medium density polyethylene (includingethylene-butene copolymers and ethylene-hexene copolymers)homo-polyethylene, polypropylene, ethylene/propylene rubbers (EPR's),ethylene/propylene/diene terpolymers (EPDM's), polybutadiene,polyisoprene and the like.

[0064] Reduced chromium oxide-on-silica catalysts represent one pathwayto improved catalyst systems for polyethylenes having characteristics ofthose typically formed using silylchromate-on-silica catalysts. It isdesired that any such catalytic system exhibit good space-time yield,producing the greatest amount of polyethylene possible with highcatalyst activity. Chromium oxide catalysts possess adequateproductivity and activity, yet polyethylenes produced through their useare less than optimal for a number of applications where high molecularweight, broad molecular weight distribution, and the presence of somedegree of bimodality of molecular weight distribution are desired.

[0065] The so-called Phillips catalyst, introduced in the early 1960swas the first chromium oxide-on-silica catalyst. The catalyst is formedby impregnating a Cr⁺³ species into silica, followed by fluidization ofthe silica matrix at ca. 400° C. -800° C. Under these conditions, Cr⁺³is converted to Cr⁺⁶. The Phillips catalyst is also commonly referred toin the prior art as “inorganic oxide-supported Cr(+6).” While chromiumoxide-on-silica catalysts exhibit good productivity, they producepolyethylenes having high molecular weight and narrow molecular weightdistribution. The so-called Phillips catalyst and related catalysts areherein referred to as “Oxo-type” catalysts. FIG. 1 gives a schematicrepresentation of the structure of Oxo-type catalysts.Silylchromate-on-silica catalysts are one type of inorganicoxide-supported Cr(+6) catalyst that produces polyethylenes not havingthe aforementioned deficiencies. Silylchromate-on-silica catalysts arereferred to herein as S-type catalysts. FIG. 2 gives a schematicrepresentation of the structure of S-type catalysts. It is and has beena goal to preserve or improve productivity of Oxo-type catalysts, whileproducing a polyethylene with molecular weight and molecular weightdistributions more closely approaching those produced with S-typecatalysts.

[0066] Variations on catalysts employing Cr⁺⁶ species supported onsilica have been known. One particular variation uses titaniumtetraisopropoxide (TTIP) impregnated onto silica along with the Cr⁺³species. Such modifications result in polyethylenes with slightlygreater molecular weight distributions. While this system producespolyethylenes tending towards those produced usingsilylchromate-on-silica type catalysts, further improvements inmolecular weight and molecular weight distribution more closelyapproaching those obtained with silylchromate-on-silica are desired.

[0067] Chromium oxide based catalysts have high activity with moderateinduction times. These catalysts make polymer with intermediatemolecular weight distribution. The inventors have found that theaddition of various silanols, in particular, triphenylsilanol, modifiesthe molecular weight distribution of polymers produced with CrOx basedcatalysts. Polymer molecular weight distribution broadens with theformation of a high molecular weight shoulder as determined by sizeexclusion chromatography (SEC). The resulting polymer looks similar to apolymer obtained with silylchromate-based catalysts.

[0068] High catalyst activity and broad polymer molecular weightdistribution are desired objectives for High Space-Time Yield (HSTY)operation. As such, there is a need to produce polymers withcharacteristics of those produced using silylchromate catalysts, butwith higher catalyst activities than those obtained using silylchromate,while maintaining the polymer molecular weight and performanceproperties of silylchromate-produced polymers.

[0069] Additionally, the use of silanols with chromium oxide catalystsare useful to tuning catalyst activity, polymer molecular weight and thebreadth of the polymer molecular weight distribution by varying theamount of silanol added. Silanol can be used with chromium oxidecatalysts in conjunction with a co-catalyst such as TEAL or DEALE. Thereagents can be added during a catalyst preparation step (“in catalyst”)or by addition to the reactor separately from the catalyst (“in situ”).The silanols of the present invention can also be used as a replacementfor silylchromate-based catalyst production. Silanols such astriphenylsilanol (TPS) added to chromium oxide-based catalyst can makesimilar catalyst as that made with silylchromate on silica. Oneadvantage of the instant approach is a realization of a reduction ofcatalyst manufacturing costs.

[0070] It has also been found that broad molecular weight distributionpolyethylenes can be made in which the comonomer can be incorporatedinto the high molecular weight component by using two chromiumcatalysts. Broad or bimodal molecular weight distribution polyethyleneis especially useful for high environmental stress crack resistant(ESCR) applications such as large part blow molding, or pipe. It hasbeen observed that some chromium oxide catalysts or chromium oxidecatalysts reduced with aluminum alkyls, such as TEAL, are capable ofvery high molecular weight polyethylene with significant comonomerincorporated. When combined with a chromium catalyst that makes a lowermolecular weight polymer with little comonomer incorporation undersimilar conditions, (e.g., silylchromate) or a chromium oxide catalysttreated with DEALE or with a silanol such as TPS plus DEALE, the desiredpolymer can be produced.

[0071] Chromium oxide catalysts activated at 600-825° C. with loadingsof 0.25-0.5 wt. % chromium on Davison 955 silica followed by reductionwith TEAL are particularly useful to make the high molecular weightcomponent (this catalyst component can also be treated with a silanol(e.g., TPS) prior to aluminum alkyl (e.g., TEAL) reduction to alsoobtain a very high molecular weight polymer). This catalyst stillincorporates comonomer at a high rate and is capable of making comonomerin situ. The low molecular weight component can be made with a highlyreduced silylchromate-type catalyst. However, the inventors have foundthat very low molecular weight polymer can be made when activatedchromium oxide catalyst is treated with TPS and then DEALE. The broadmolecular weight distribution can be made by blending the polymercomponents made individually by each catalyst system or by firstblending the catalysts and then making the mixed polymers during thepolymerization reaction. The inventors have found that a very broadmolecular weight distribution can be obtained without an excessiveincrease in the z-average molecular weight (M_(z)) component. This isparticularly important to allow for high ESCR without a significantincrease in polymer swell.

[0072] While in many of the examples that follow, DEALE is used, otheraluminum alkyls may be used. Similarly, where DEALE is used, it shouldbe understood that other alkyl aluminum alkoxides may be used and whereTPS is used, other silanols may be substituted. In general, the alkylgroups of the aluminum alkyl can be the same or different, and shouldhave from about 1 to about 12 carbon atoms and preferably 2 to 4 carbonatoms. Examples include, but are not limited to, triethylaluminum,tri-isopropylaluminum, tri-isobutyl aluminum, tri-n-hexyl aluminum,methyl diethylaluminum, and trimethylaluminum. Although the examplesfocus primarily on the use of TEAL, it should be understood that theinvention is not so limited. In general, the alkyl aluminum alkoxide,having the general formula R₂-Al-OR where the alkyl groups may be thesame or different, should have from about 1 to about 12 carbon atoms andpreferably 2 to 4 carbon atoms. Examples include but are not limited to,diethyl aluminum ethoxide, diethyl aluminum methoxide, dimethyl aluminumethoxide, di-isopropyl aluminum ethoxide, diethyl aluminum propoxide,di-isobutyl aluminum ethoxide, and methyl ethyl aluminum ethoxide.Although the examples almost exclusively use DEALE, it should beunderstood that the invention is not so limited. Additionally withrespect to the silanols useful in the present invention, a number ofsilanols may be used. These include triphenyl silanol, methyl diphenylsilanol, trimethyl silanol, triethyl silanol, triisobutyul silanol, aswell as others.

[0073] Table 1 lists several exemplary commercial silica supports withtheir physical properties. These silica supports are illustrativeexamples and not exhaustive of the types of silica which may be used inthe present invention. Other silica supports commonly used in the fieldand known to those of skill in the art are also useful herein. Table 1provides approximate pore volume, surface area, average pore diameter,average pore size and percent titanium for the silica supports used inthis study. The label is that used by the supplier to describe thesupport. The number without the parentheses is the name of the supportsupplied as silica alone. The number in parentheses is the name of thesupport when it is supplied with a chromium salt already impregnated onthe support. Although these silicas were obtained from the suppliers anysilica fitting the specifications below would be expected to function ina similar manner. The present invention is not limited to any specificcommercial silica support but may be used with any silicas having a porevolume of about 1.1-1.8 cm³/g and a surface area of about 245-375 m²/g;or a pore volume of about 2.4-3.7 cm³/g and a surface area of about410-620 m²/g; or a pore volume of about 0.9-1.4 cm³/g and a surface areaof about 390-590 m²/g. TABLE 1 Commercial Silica Supports and PhysicalProperties Average Average Pore Surface Pore Pore Silica Volume AreaDiameter Size Support (cm³/g) (m²/g) (Å) (μm) Ti (%) Grace 955 1.45 310210 55 — (957) PQ MS3050 3.02 513 198 90 — (35100) Ineos EP52 1.15 49090 70 2.60 (352)

[0074] General Catalyst Preparations

[0075] Unless otherwise noted the catalysts used in the followingexamples were all made by the following procedures.

[0076] General Preparation A. Chromium oxide catalyst activation:Catalysts were received from the suppliers with the chromium alreadyimpregnated on the supports. The catalyst physical properties aredescribed in Table 1. Activation is conducted by passing gas through thecatalyst for four hours at the specified temperature in dry air. This isusually conducted in a tube furnace. The catalyst is then stored undernitrogen until used.

[0077] General Preparation B Chromium oxide catalyst treatment: In atypical preparation 3 grams of previously activated catalyst is placedin a 50 mL airless ware flask with a stir bar under inert atmosphere.Thirty-five mL of dry degassed hexane is added and the mixture is heatedto 50° C. The silanol is then added via syringe. The mixture is stirred2 hours followed by alkylaluminum addition, when used (all reagents are20-25 wt. % in hexane). The stated equivalents are always the ratio ofreagent to chromium. After 30 minutes, drying is commenced. This can bedone under high vacuum or with a nitrogen purge. Catalyst is storedunder nitrogen until used.

[0078] Catalyst Descriptions

[0079] When used, the ratio of reagents to chromium added can be foundin the example; “in reactor” means the catalyst was added separatelyfrom the catalyst. “On catalyst” means the reagent is added in acatalyst preparation step.

Example 1

[0080] The catalyst was used as supplied by Davison Chemical andconsists of 0.5 wt. % chromium on Davison 955 silica and was activatedat 825° C. (General preparation A). See silica specifications in Table1.

Examples 2-3

[0081] The catalyst is the same as that used in Example 1 except thatTPS is added in a catalyst preparation step as in General preparation B.

Examples 4-6

[0082] The catalysts are the same as examples 1-3 except the silicacontained only 0.25 wt. % chromium and was activated at 600° C.

Examples 7-8

[0083] The catalyst is the same as that used in example 1 except thecatalyst was activated at 600° C.

Examples 9-10

[0084] The catalyst consists of 0.5 wt. % Cr on Davison 955 silica (200°C. dehydration) treated with titanium tetra-isopropoxide prior toactivation. Enough TTIP is added so after activation 3.8 wt. % Tiremains (see U.S. Pat. No. 4,011,382 for specific procedures for TTIPaddition). Activation was done at 825° C. TPS was added in reactor.

Examples 11-12

[0085] Same catalyst as that used in example 9.

Examples 13-16

[0086] Same catalyst as that used in example 1. When used on catalystTPS and DEALE are added as in General prep B.

Examples 17-18

[0087] The catalyst is the same as that used in example 7.

Example 19-22

[0088] The catalyst is the same as that used in example 4. When used oncatalyst, TPS and DEALE are added as in General prep B.

Examples 23-24

[0089] The catalyst is the same as that used in example 9.

Example 25

[0090] The catalyst is the same as that used in example 1 treated withTPS and triisobutyl aluminum (TIBA) as in General prep B.

Examples 26-29

[0091] The catalyst is the same as that used in example 1. When used,DEALSi is added to the reactor separately. DEALSi is formed by mixing inhexane equal molar amounts of triethylsilanol and triethylaluminum

Examples 30-32

[0092] The catalyst is the same as that used in example 9. When used,DEALSi is added to the reactor separately.

Examples 33-35

[0093] The catalyst used is MS35100 which is a chromium oxide catalyston MS 3050 silica obtained from PQ with the specifications listed inTable 1. The catalyst contains 0.5 wt. % Cr. The catalyst is activatedat 700° C. (General preparation A). When used on catalyst, TPS and DEALEare added as in General prep B.

Example 36

[0094] The catalyst is the same as that used in example 4 treated with 2equivalents of TEAL as in General prep B.

Example 37

[0095] The catalyst is the same as that used in example 7 treated withTPS and DEALE as in General prep. B.

Example 38

[0096] Equal weight amounts of the catalysts from examples 36 and 37 areused here.

Example 39

[0097] Catalyst preparation: 3.59 grams of previously dehydrated 955silica is placed in a 50 mL airless ware flask with a stir bar underinert atmosphere. Next 0.112 grams of bis-triphenylsilyl chromate isadded. Thirty-five mL of dry degassed hexane is added and the mixture isheated to 50° C. The mixture is stirred for 2 hours, then 10 equivalentsof DEALE is added. After 30 minutes at 50° C., the mixture is driedunder high vacuum.

[0098] Lab Slurry Procedure

[0099] A one liter stirred reactor was used for the polymerizationreactions. The reactor was thoroughly dried under a purge of nitrogen atelevated temperatures before each run. 500 mL of dry degassed hexane wasfed to the reactor at 60° C. If used, hexene is added at this point.Unless otherwise noted 10 mL of 1-hexene is used in each experiment. Asmall quantity (0.1-0.25g) of Davison 955 silica dehydrated at 600° C.and treated with 0.6 mmole/g of TEAL is then added to the reactor topassivate any impurities. No TEAL treated silica was added in any runwhere a reagent was added to the reactor separately from the catalyst.After stirring for 15 minutes the catalyst is charged followed byadditional reagents. When silanols and alkylaluminum reagents are addedseparately to the reactor from the catalyst, the silanol is added firstfollowed by the addition of the alkyaluminum. Both are added as dilutehexane solutions. The reactor is sealed and hydrogen is charged at thispoint. Hydrogen is only used where noted in the tables. The reactor ischarged to 200 psi with ethylene. Ethylene is allowed to flow tomaintain the reactor pressure at 200 psi. Ethylene uptake is measurewith an electronic flow meter. All copolymerizations were run at 85° C.Polymerizations were run until a maximum of 160 grams polyethylene weremade or terminated sooner. The reactor was opened after depressurizationand the temperature lowered. The polymer weight was determined afterallowing the diluent to evaporate. The polymer was then characterizedemploying a number of tests.

[0100] Tests

[0101] Density: ASTM D-1505.

[0102] Melt Index: (12) ASTM D-2338 Condition E measured at 190° C.reported as grams per 10 minutes.

[0103] Flow Index: (I21) ASTM D-1238 Condition F measured at 190° C.using 10 times the weight as used in Melt Index above.

[0104] MFR: Melt Flow ratio is the Flow index/Melt index.

[0105] SEC: Polymer Laboratories instrument; Model: HT-GPC-220, Columns:Shodex, Run Temp: 140° C., Calibration Standard: traceable to NIST,Solvent: 1,2,4-Trichlorobenzene. Mn and Mw values in the tables shouldbe multiplied by 10³. Mz values multiplied by 10⁶.

[0106] BBF: Butyl branching frequency as measured by ¹³C-NMR. The valueis the number of butyl branches per 1000 carbon atoms.

[0107] Effect of Silanol on CrOx Catalyst: Molecular WeightDistribution, Molecular Weight, and Productivity

[0108] The effect of adding arylsilanol to chromium oxide catalystsystems was studied using chromium oxide (0.5 wt.%) loaded onto 955-typesilica activated at 825° C. (see Table 2, examples 1-3), having a porevolume of about 1.1-1.8 cm³/g and a surface area of about 245-375 m²/g.TPS was used as the arylsilanol in this example. A clear trend inbroadening molecular weight distribution (Mw/Mn) is seen when 2equivalents of TPS are added, relative to that seen for 1 equivalent ofTPS and in the absence of TPS. An increase in Mz/Mw indicates the growthof a high molecular weight shoulder as TPS is added. Polymer density wasobserved to increase when TPS was added indicating lower comonomerincorporation. Desired densities of about 0.918-0.970 g/cm³, amongothers, of the resulting polymers may be so obtained. BBF measurementsconfirm lower comonomer incorporation (see Table 2). Polymer molecularweight also increases. Catalyst activity is found to decrease as theamount of TPS is increased. Lower catalyst activity is due to acombination of longer induction times and lower inherent activity (FIG.3). TABLE 2 Effect of Triphenyl Silanol (TPS) on Oxo Chromium CatalystTPS Bulk Exam- added to Time YIELD Flow Act.gPE/ Density Mw/ Mz/ plescatalyst (min) (g) Index gcat-1 hr (g/cc) Mn Mw Mz Mn Mw BBF CrOx on 955Silica/0.5 wt % Cr; 825 C. activation 1 none 58 153 2.6 1,429 0.34 25.1243 1.09 9.68 4.47 3.7 2 1 eq. 80 161 2.1 607 0.42 21.4 283 1.46 13.265.17 2.9 3 2 eq. 160 101 2.6 102 0.35 10.3 348 2.16 33.90 6.22 1.9

[0109]FIG. 4 illustrates the molecular weight plots (data obtained bySEC) for polymers made with CrOx with no TPS (FIG. 4a); CrOx with 1equivalent of TPS (FIG. 4b); and CrOx with 2 equivalents of TPS (FIG.4c) (examples 1-30). The high molecular weight shoulder becomespronounced for polymer produced with CrOx catalyst in the presence of 2equivalents of TPS. Although not readily apparent from the figures, thehigh molecular weight shoulder also increases in magnitude in going frompolymer produced in the absence of TPS to that produced in the presenceof 1 equivalent of TPS. This trend is evidenced by the increase inM_(z)/M_(w) values of 4.47 and 5.17, respectively for polymer producedwith CrOx in the absence of TPS and that produced with CrOx in thepresence of 1 equivalent of TPS. Polymer MWD can be varied bycontrolling the amount of arylsilanol added to the catalyst. TABLE 3Effect of Triphenyl Silanol (TPS) on Oxo Chromium Catalyst Catalyst andExam- TPS addition Time YIELD Act.gPE/ Mw/ Mz/ Den. ples method (min)(g) FI gcat-1 hr BD Mn Mw Mz Mn Mw g/cc CrOx on 955 Silica/0.25 wt % Cr;600 C. activation 4* no TPS 72 174 1.1 765 0.28 18.1 356 1.79 20 5.00.9360 5 1 eq. TPS 118 143 1.1 274 0.35 15.6 409 1.92 26 4.7 0.9423 oncatalyst 6 2 eq. TPS 300 78 3.8 30 0.26 11.6 327 1.68 28 5.1 0.9447 oncatalyst CrOx on 955 Silica/0.50 wt % Cr; 600 C. activation 7 no TPS 110154 5.6 1,074 0.32 14.9 294 1.54 20 5.2 0.9402 8 1 eq. TPS 94 179 1.0472 0.32 15.6 368 1.71 24 4.7 0.9407 in reactor TiCrOx on 955 Silica/0.5wt % Cr; 825 C. activation 9 no TPS 62 156 3.8 1,497 0.32 12.6 212 0.8817 4.2 0.9466 10 1 eq. TPS 65 161 6.1 612 0.29 10.1 234 1.27 23 5.40.9470 in reactor

[0110] In Table 3 (examples 4-6), data is presented for CrOx on 955-typesilica at a loading of 0.25 wt. % chromium and activated at 600° C. inthe absence of TPS; in the presence of 1 equivalent of TPS; and in thepresence of 2 equivalents of TPS. Also shown is data for CrOx on955-type silica at a loading of 0.5 wt. % chromium and activated at 600° C. in the absence of TPS and in the presence of 1 equivalent of TPSadded in situ. Finally, there is data for titanated chromium oxide on955-type silica activated at 825° C. in the absence of TPS and with 1equivalent of TPS added in situ. The effect of TPS is apparent.Molecular weight distribution broadens but without a significantincrease in the high molecular weight tail. In examples 4-10 thecatalyst induction periods were observed to increase when TPS is added(FIG. 5). FIG. 5(a) shows chromium oxide on 955-type silica activated at600° C.; FIG. 5(b) shows titanated chromium oxide on 955-type silicaactivated at 825° C.

[0111] In comparison with the above-presented data, it can be seen thatthe molecular weight effects are catalyst-specific. In the presentexample, molecular weight distribution is broadened, but the highmolecular weight shoulder was not enhanced; in the earlier example, theaddition of TPS both broadened the molecular weight distribution andincreased the intensity of the high molecular weight shoulder.

[0112] In Table 4 (examples 11-14), data is presented fortriethylsilanol (TES) addition to chromium oxide catalysts in ethylenepolymerization reactions. Separate addition of TES to polymerizationreactions catalyzed with titanated chromium oxide on 955 type silica andchromium oxide on 955 type silica, both with 0.5 wt. % chromium andactivated at 825C., led to much reduced activity and little or no changein polymer molecular weight distribution. In FIG. 6 it can be seen thatTES addition leads to longer induction periods and lower activitylevels. This shows that not only is this technology catalyst specific,it is also silanol specific. TABLE 4 Addition of TES to Chromium OxoCatalysts Catalyst and TEX Exam- addition Time YIELD Act.gPE/ Act.gPE/Mn Mw Mz Mw/ Mz/ Den. ples method (min) (g) FI gcat-1 hr gcat-1 hr(×10³) (×10³) (×10⁶) Mn Mw g/cc TiCrOx on 955 Silica/0.5 wt % Cr; 825 C.activation 11 no TES 67 165 12.2 1,309 0.23 9.4 170 0.75 18 4.4 0.940312 1 eq. TES 97 162 7.7 386 0.27 12.7 231 1.27 18 5.5 0.9469 in reactorCrOx on 955 Silica/0.5 wt % Cr; 825 C. activation 13 no TES 59 1011643.8 1,416 0.28 22.7 271 1.38 12 5.1 0.9399 14 1 eq. TES 110 160 2.1 3380.28 22.1 302 1.52 14 5.0 0.9398 in reactor

[0113] Alkyl silanols also provide for useful chemistry when alkylaluminum 10 alkoxides are used with CrOx-type catalysts. The addition ofsilanols and alkyl aluminum alkoxides can be used to convert CrOxcatalysts and titanated CrOx catalysts into catalyst systems providingperformance similar to silylchromate-based catalyst systems.Silylchromate-based catalysts generally produce desirable polyethylenesrelative to those produced by chromium oxide-type catalysts.Silylchromate produced polyethylenes generally have a broader molecularweight distribution than those produced using chromium oxide-typecatalysts. The broader molecular weight distribution leads to betterprocessability of the resulting polyethylene. However, theproductivities of silylchromate-based catalysts are typically muchpoorer than those realized using chromium oxide-based catalysts. TABLE 5Effect of TPS and Alkylaluminum Compounds of Chromium Oxo CatalystsCatalyst and Exam- modifiers H2 Time YIELD Act.gPE/ Den. ples additionmethod (scc) (min) (g) FI gcat-1 hr BD Mn Mw Mz DI Z/W g/cc CrOx on 955Silica/ 0.5 wt % Cr; 825 C. activation 15 none 0 79 174 2.4 1,250 0.3226.4 268 1.33 10.1 5.0 0.9425 16 1 eq. TPS + 5 eq. 0 49 126 47.5 1,5230.30 10.7 197 2.03 18.5 10.3 0.9622 DEALE in catalyst CrOx on 955Silica/ 0.5 wt % Cr; 600 C. activation 17 none 500 110 154 5.6 1,0740.32 14.9 294 1.54 20.0 5.2 0.9402 18 1 eq. TPS + 5 eq. 500 116 120 14.8490 0.33 13.8 278 1.93 20.1 6.9 0.9583 DEALE in reactor CrOx on 955Silica/ 0.25 wt % Cr; 600 C. activation 19*  none 500 72 174 1.1 7650.28 18.1 356 1.79 19.6 5.0 0.9360 20 1 eq. TPS + 5 eq. 500 71 154 38.7590 0.37 8.3 192 2.00 23.2 10.4 0.9595 DEALE in reactor 21 2 eq. TPS + 5eq. 500 78 156 29.5 309 0.41 7.8 212 1.88 27.3 8.9 0.9594 DEALE inreactor 22 1 eq. TPS + 5 eq. 500 34 153 148.1 1,211 0.38 DEALE incatalyst TiCrOx on 955 Silica/ 0.5 wt % Cr; 825 C. activation 23 none500 64 175 9.7 1,380 0.32 9.8 182 0.81 18.5 4.47 0.9471 24 1 eq. TPS + 5eq. 500 72 176 42.2 703 0.29 7.8 196 1.66 25.0 8.47 0.9599 DEALE inreactor CrOx on 955 Silica/ 0.5 wt % Cr; 825 C. activation 25 1 eq.TPS + 5 eq. 500 72 145 5.4 496 0.31 0.9501 TIBA in catalyst

[0114] Table 5 illustrates the effect of the addition of silanol andalkyl aluminum alkoxide to chromium oxide-based catalyst on 955-typesilica. Polymerizations without silanol or any organoaluminum iscompared with analogous systems having 5 equivalents of DEALE and 1equivalent of TPS added to the catalyst. (0.5 wt. % of chromium loadingand activated at 825° C.; examples 15 and 16). Significant increase inpolymer flow index and polymer molecular weight distribution accompaniedby a high molecular weight shoulder (very high Mz/Mw) can be seen.Addition of alkyl aluminum alkoxide and alkyl silanol can be used tocontrol these parameters. Although values outside this range areattainable, desirable flow index values from about 1-500 can beachieved. Catalyst activity is also observed to increase and catalystinduction period normally associated with TPS addition is eliminated.The combination of the TPS and DEALE produce the desired polymermolecular weight distribution while decreasing catalyst induction timecompared to that found without DEALE addition (FIG. 7). The samecomparison can be seen in Examples 17 and 18 except that the catalystactivation was conducted at 600° C. and the TPS and DEALE were added tothe reactor. The polymer molecular weight drops, the molecular weightdistribution remains the same but the high molecular weight shoulder isseen to increase. In examples 19 to 22, the same catalyst is used as inthe previous examples except that the chromium loading is 0.25 wt. %.When TPS and DEALE are added to the reactor (examples 20 and 21), thepolymer molecular weight is observed to decrease, molecular weightdistribution increases and the high molecular weight shoulder increases(higher Mz/Mw) compared to the unmodified catalyst. When the componentswere added to the catalyst (example 22), higher catalyst activity andpolymer flow index values were found. Utility lies in the ability tocontrol these parameters, allowing one a greater ability to tailor thecharacteristics of the polymer produced.

[0115] In Example 24 separate addition of TPS and DEALE to apolymerization reaction using titanated chromium oxide catalyst (0.5 wt.% Cr) on 955 type silica activated at 825° C. was conducted. Incomparison to the same reaction without TPS and DEALE (example 23),polymer molecular flow index is observed to increase, moleculardistribution increases and the high molecular weight shoulder increases(higher Mz/Mw).

[0116] In Example 25 it can be seen that other alkyl aluminum reagentscan be used in conjunction with chromium oxide catalysts and TPS. Inthis example, the same catalyst is used as in example 16 is used exceptthat triisobutyl aluminum (TIBA) is used in place of DEALE. When TIBA isused in place of DEALE higher molecular weight polymers are obtained.

[0117] Although the specific silica supported chromium oxide catalystmay affect results, it can be seen that when alkyl aluminum or alkylaluminum alkoxides are used with TPS, lower molecular weight polymerswith broader molecular weight distributions and increased high molecularweight shoulders can be obtained without unacceptable losses in catalystactivity due to long induction times and lower activities as found withTPS and chromium oxide catalysts alone. Polymer molecular weights aretoo high for most product applications in the absence of alkyl aluminumand alkyl aluminum alkoxides.

[0118] The addition of diethylaluminum triethylsiloxide (DEALSi) tochromium oxide or titanated chromium oxide catalyst yields resultssimilar to those obtained using silylchromate-based catalysts.Generally, higher productivities for the catalysts, and higher molecularweights for the resulting polyethylenes are obtained when using chromiumoxide or titanated chromium oxide catalyst in the presence of DEALSi.DEALSi is the reaction product of one equivalent each of triethylsilanol and triethyl aluminum. As DEALSi is added spanning the range of2 to 5 and 10 equivalents, an increase in polymer flow index isobserved. (Table 6, examples 26 through 32). Induction time is alteredand the kinetic profile shows an elimination of induction time in thepresence of DEALSi (see FIG. 8). Additionally, the data in Table 6 showsthat polyethylenes having broader molecular weight distribution and amore pronounced high molecular weight shoulder result from theintroduction of DEALSi into chromium oxide-based catalyst systems.Addition of TES alone to chrome oxide catalysts as shown in Table 4 didnot modify polymer properties and significantly poisoned the catalysts.The reaction product of TEAL and TES in conjunction with specificcatalysts allows for high catalyst activities, improved flow indexresponse and polymer molecular weight distribution. TABLE 6 Effect ofDEALSi on Chromium Oxo Catalysts DEALSi Exam- in situ Time YIELD FlowAct.gPE/ Den. ples addition (min) (g) Index gcat-1 hr BD Mn Mw Mz DI Z/Wg/cc CrOx on 955 Silica/0.5 wt % Cr; 825 C. activation 26 none 59 1643.8 1,416 0.28 22.7 271 1.38 12.0 5.07 0.9399 27 2 eq. 56 151 29.9 1,1010.33 0.9554 28 5 eq. 55 147 34.4 1,027 0.35 10.7 160 1.46 15.0 9.130.9540 29 10 eq. 63 141 42.3 975 0.33 0.9562 TiCrOx on 955 Silica/0.5 wt% Cr; 825 C. activation 30*  none 67 165 12.2 1,309 0.23 9.4 170 0.7518.0 4.42 0.9403 31 2 eq. 80 169 34.4 838 0.35 0.9558 32 5 eq. 68 14321.5 814 0.32 8.5 170 1.38 20.1 8.08 0.9564

[0119] Table 7 illustrates the effect of the addition of silanol andalkyl aluminum alkoxide to chromium oxide-based catalyst on MS 3050-typesilica (0.5 wt. % of chromium loading and activated at 700° C.).Addition of TPS and DEALE either in the reactor or on the catalystresults in increased activity and a lowering of polymer molecular weight( examples 34 and 35). Polymer molecular weight distribution did notchange but the high molecular shoulder increased significantly based onMz/Mw values. The activity increased due to elimination of the inductionperiod. Without TPS and DEALE addition this catalyst produces polymerwith very low flow index indicative of unacceptably high polymermolecular weight (examples 33).

[0120] The results in Table 7 show that more than one kind of silicaresponds in the same manner to addition of silanols and alkylaluminumalkoxides. TABLE 7 Effect of TPS and Alkyl Aluminum Compounds onChromium Oxo Catalyst on MS 3050 Silica Exam- H2 Time YIELD Act.gPE/Den. ples Catalyst and modifiers addition method (scc) (min) (g) FIgcat-1 hr BD Mn Mw Mz DI Z/W g/cc CrOx on MS3050 silica/0.5 wt % Cr; 700C. activation 33 none 500 82 212 1.4 695 0.35 20.9 452 2.27 21.60 5.010.9411 34 1 eq. TPS + 5 eq. DEALE in reactor 500 54 188 38.0 864 0.3510.2 190 1.81 18.50 9.56 0.9585 35 1 eq. TPS + 5 eq. DEALE in catalyst500 32 179 64.7 1,978 0.38 0.9613

[0121] Effect of Silanol on Bimodality of Molecular Weight Distribution.

[0122] The molecular weight manipulations made possible by the presentinvention can be extended through the use of dual chromium-basedcatalysts to increase the level of bimodality in the resultingpolyethylene. It is desirable to produce a high density polyethylene inwhich the side chain branching is primarily found only in the highmolecular weight shoulder component of the polymer. This is achievedthrough the use of a dual catalyst system employing two chromium basedcatalysts. In one example, there is a catalyst based on chromium oxideon silica or chromium oxide on silica that can be reduced with atrialkyl aluminum compound such as TEAL. The second catalyst is chromiumoxide treated with TPS and DEALE. Table 8 provides results forpolyethylenes produced with each catalyst separately and with this dualcatalyst system all under the same reaction conditions. The use of aTEAL reduced chromium oxide catalyst on 955 silica and activated at 600°C. (example 36) resulted in the formation of polymer with very highmolecular weight (Mw>390,000). The density shows that a significant ofcomonomer was incorporated in the polymer. The use of chromium oxidecatalyst on 955 silica and activated at 600° C. followed by treatmentwith TPS and DEALE (example 37) results in formation of polymer withvery low molecular weight (Mw<115,000). The polymer density is very highapproaching homopolymer levels indicating little or none comonomer wasincorporated into the polymer. Employment of equal amounts of eachcatalyst (example 38) resulted in formation of a polymer withintermediate molecular weight and density, but with broader molecularweight distributions. This shows that both catalysts were active andthat the high molecular weight portion of the polymer would contain thecomonomer. In example 39 is seen another catalyst capable of producinglow molecular weight polymer with low comonomer incorporation rates.This silylchromate based catalyst that has been reduced with high levelof DEALE can be used in conjunction with the chromium oxide catalystsdescribed above that make the high molecular weight, high comonomercontaining component. TABLE 8 Dual Chromium Catalyst System for BimodalHDPE Exam- Catalyst Time YIELD Flow Act.gPE/ Mw Mz Den. ples Catalystmodification (min) (g) Index gcat-1 hr BD Mn Mw Mz Mn Mw g/cc IndividualCatalyst Components 36 CrOx on 955 Silica/ 2 eq. TEAL 47 166 0.6 8650.35 17.5 393 1.76 22.4 4.5 0.9430 0.25 wt % Cr; 600 C. activation 37CrOx on 955 Silica/ 1 eq. TPS 36 153 205.5 1,028 0.40 6.8 114 1.21 16.810.5 0.9623 0.5 wt % Cr; 2 eq. DEALE 600 C. activation Catalyst Blend 381:1 ratio of 69 163 7.1 659 0.34 8.9 292 1.56 33.0 5.3 0.9509 catalystsfrom examples 32 and 33 39 Silychromate (0.24 10 eq. DEALE 47 155 87.0788 0.36 0.9638 wt. %) on 955 on catalyst silica dehydrated at 600 C.

[0123] The dual catalyst system produces a polyethylene having a verybroad molecular weight distribution with comonomer incorporation inhigher concentration in the high molecular weight region of thedistribution. Polymer made with the dual catalyst system would beexpected to have improved ESCR properties as well as improved pipeproperties.

[0124] Although the present invention and its advantages have beendescribed in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the invention as defined by the appended claims.Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

1. A supported chromium catalyst comprising: chromium oxide, asilica-containing support comprising silica selected from the groupconsisting of silica having: (a) a pore volume of about 1.1-1.8 cm³/gand a surface area of about 245-375 m²/g; (b) a pore volume of about2.4-3.7 cm³/g and a surface area of about 410-620 m²/g; and (c) a porevolume of about 0.9-1.4 cm³/g and a surface area of about 390-590 m²/g;and, an alkyl silanol, wherein said supported chromium catalyst isactivated at 400-860° C., prior to the addition of said alkyl silanol.2. The catalyst of claim 1 further comprising titaniumtetraisopropoxide.
 3. The catalyst of claim 1 further comprising anorganoaluminum compound.
 4. The catalyst of claim 3 wherein saidactivated chromium catalyst is treated first with said alkyl silanol andthen with said organoaluminum compound.
 5. The catalyst of claim 3wherein said silica has a pore volume of about 2.4-3.7 cm³/g and asurface area of about 410-620 m²/g and said organoaluminum compound isan alkyl aluminum alkoxide compound.
 6. The catalyst of claim 3 whereinsaid silica has a pore volume of about 1.1-1.8 cm³/g and a surface areaof about 245-375 m²/g, and said organoaluminum compound is an alkylaluminum alkoxide compound.
 7. The catalyst of claim 3 wherein saidorganoaluminum compound is added in-situ.
 8. The catalyst of claim 3further comprising at least a second chromium-based compound.
 9. Thecatalyst of claim 8 wherein said second chromium-based compound is achromium oxide on silica or an organoaluminum-reduced chromium oxide onsilica.
 10. The catalyst of claim 3 wherein said alkyl silanol or saidorganoaluminum compound or both said alkyl silanol and saidorganoaluminum compound are added in-situ.
 11. The catalyst of claim 10wherein said alkyl silanol and said organoaluminum compound arepre-mixed prior to said in-situ addition.
 12. The catalyst of claim 3wherein said organoaluminum compound is an alkyl aluminum alkoxidecompound.
 13. The catalyst of claim 12 wherein said alkyl aluminumalkoxide compound is diethyl aluminum ethoxide.
 14. The catalyst ofclaim 12 formed by the in situ addition of said alkyl aluminum alkoxidecompound.
 15. The catalyst of claim 14 wherein said alkyl aluminumalkoxide compound is diethyl aluminum ethoxide.
 16. The catalyst ofclaim 3 wherein said organoaluminum compound is an alkyl aluminumcompound.
 17. The catalyst of claim 16 wherein said alkyl aluminumcompound is selected from the group consisting of triethyl aluminum,tri-isobutyl aluminum, and tri-n-hexyl aluminum.
 18. The catalyst ofclaim 17 formed by the in situ addition of said alkyl aluminum compound.19. The catalyst of claim 17 wherein said alkyl aluminum compound istri-isobutyl aluminum.
 20. The catalyst of claim 1 wherein saidsupported chromium catalyst is activated at 600-860° C.
 21. The catalystof claim 1 wherein said alkyl silanol is triphenyl silanol
 22. Asupported chromium catalyst comprising: chromium oxide, asilica-containing support comprising silica selected from the groupconsisting of silica having: (a) a pore volume of about 1.1-1.8 cm³/gand a surface area of about 245-375 m²/g; (b) a pore volume of about2.4-3.7 cm³/g and a surface area of about 410-620 m²/g; and (c) a porevolume of about 0.9-1.4 cm³/g and a surface area of about 390-590 m²/g;and, an organoaluminum compound, wherein said supported chromiumcatalyst is activated at 400-860° C.
 23. The catalyst of claim 22wherein said organoaluminum compound is diethyl aluminumtriethylsiloxide.
 24. The catalyst of claim 22 further comprisingtitanium tetraisopropoxide.
 25. A supported chromium catalystcomprising: chromium oxide, a silica-containing support comprisingsilica selected from the group consisting of silica having: (a) a porevolume of about 1.1-1.8 cm³/g and a surface area of about 245-375 m²/g;(b) a pore volume of about 2.4-3.7 cm³/g and a surface area of about410-620 m²/g; and (c) a pore volume of about 0.9-1.4 cm³/g and a surfacearea of about 390-590 m²/g; wherein said supported chromium catalyst isactivated at 400-860° C.; and, a second chromium-based compoundcomprising silylchromate on silica treated with an organoaluminumcompound.
 26. The catalyst of claim 25 wherein said chromium oxidecatalyst component is treated with an organoaluminum compound afteractivation.
 27. The catalyst of claim 25 further comprising titaniumtetraisopropoxide.
 28. A process for producing an ethylene polymercomprising the steps of: contacting ethylene under polymerizationconditions with a catalyst system, said catalyst system comprisingchromium oxide, an alkyl silanol compound, and a silica-containingsupport comprising silica selected from the group consisting of silicahaving: (a) a pore volume of about 1.1-1.8 cm³/g and a surface area ofabout 245-375 m²/g; (b) a pore volume of about 2.4-3.7 cm³/g and asurface area of about 410-620 m²/g; and (c) a pore volume of about0.9-1.4 cm³/g and a surface area of about 390-590 m²/g; and, controllingone or more of catalyst activity, polymer Mz/Mw, polymer Mw/Mn, andpolymer density of the resulting ethylene polymer by varying the levelof addition of said alkyl silanol.
 29. The process of claim 28 whereinsaid polymer Mw/Mn is controlled to greater than about 15 and saidpolymer Mz/Mw is controlled to greater than about
 5. 30. The process ofclaim 28 wherein said catalyst system further comprises anorganoaluminum compound.
 31. The process of claim 30 wherein saidcatalyst system further comprises at least a second chromium-basedcatalyst.
 32. The process of claim 31 wherein said second chromium-basedcompound is a chromium oxide on silica or an organoaluminum-reducedchromium oxide on silica.
 33. The process of claim 30 wherein saidorganoaluminum compound is an alkyl aluminum alkoxide.
 34. The processof claim 33 wherein said alkyl aluminum alkoxide comprisesdiethylaluminum ethoxide.
 35. The process of claim 30 wherein saidorganoaluminum compound is an alkyl aluminum compound.
 36. The processof claim 35 wherein said alkyl aluminum compound is selected from thegroup consisting of triethyl aluminum, tri-isobutyl aluminum, andtri-n-hexyl aluminum.
 37. The process of claim 28 wherein said catalystsystem further comprises titanium tetraisopropoxide.
 38. A process forproducing an ethylene polymer comprising the steps of: contactingethylene under polymerization conditions with a catalyst system, saidcatalyst system comprising chromium oxide, a silica-containing supportcomprising silica selected from the group consisting of silica having:(a) a pore volume of about 1.1-1.8 cm³/g and a surface area of about245-375 m²/g; (b) a pore volume of about 2.4-3.7 cm³/g and a surfacearea of about 410-620 m²/g, and (c) a pore volume of about 0.9-1.4 cm³/gand a surface area of about 390-590 m²/g; wherein said supportedchromium catalyst is activated at 400-860° C.; and, a secondchromium-based compound comprising silylchromate on silica treated withan organoaluminum compound; and, controlling one or more of polymermolecular weight, polymer Mz/Mw, polymer Mw/Mn, and distribution ofcomonomer incorporation by varying the relative amount of each of saidchromium oxide and said second chromium-based compound.
 39. The processof claim 38 wherein said chromium oxide catalyst component is treatedwith an organoaluminum compound after activation.
 40. The process ofclaim 38 wherein said catalyst system further comprises titaniumtetraisopropoxide.
 41. An ethylene polymer having a density of0.918-0.970 g/cm³ and a flow index (I₂₁) of 1-500 and produced by theprocess of claim
 28. 42. An ethylene polymer having a density of0.918-0.970 g/cm³ and a flow index (I₂₁) of 1-500 and produced by theprocess of claim
 30. 43. An ethylene polymer having a density of0.918-0.970 g/cm³ and a flow index (I₂₁) of 1-500 and produced by theprocess of claim
 31. 44. An ethylene polymer having a density of0.918-0.970 g/cm³ and a flow index (I₂₁) of 1-500 and produced by theprocess of claim
 32. 45. An ethylene polymer having a density of0.918-0.970 g/cm³ and a flow index (I₂₁) of 1-500 and produced by theprocess of claim 38.